Philips flat-panel dead. Replaced PSU caps and still squealing

[puttsy]

Long time lurker, first time poster. Not sure why I didn't already have an account here before today though...hmm.

Well, I've recapped some gear in my time and when I came to this TV, I did nothing less. Replaced the caps directly around the power source (the common problem, 200v caps)and the problem still presists. When the TV is plugged in, there is a high pitched whine/squeal that decreases in pitch over a short time.

Nothing seems to have changed after replacing the caps so it leads me to wonder what the next place to deal with is.

TV model is: 22PFL3504D/F7

Beyond capacitors, my experience on PCB's is limited so some liberal explanations may not hurt. I've recapped many types of gear and solved the problems in most but, after recapping failed to solve the problem here, I'm looking to learn the next step!

Although I would prefer to replace all the caps, I couldn't make it happen on this order because, well, I don't want to stick $50 bucks into caps if it's something else. If there are other components that, in your valuable experience, present similar symptoms, would it be advantageous to replace those or will it be a snipe hunt to get to the bottom of it?

[Mr Bill]

Re: Philips flat-panel dead. Replaced PSU caps and still squealing

Can you get a few pictures of the power board. Is the power supply and main tuner all one board? Is the tv chirping? From my past experience it'll do a long squeel then chirp chirp chirp. This has been posted a few times but not on your model, atleast i don't think but it always turns out to be a bad zener diode. So that would be a good place to start.

[RON_CET]

Re: Philips flat-panel dead. Replaced PSU caps and still squealing

check for shorted zener d668 20volt 1 watt on psu,if you find shorted on board,desolder and remove and check also off board

[puttsy]

Re: Philips flat-panel dead. Replaced PSU caps and still squealing

Can you get a few pictures of the power board. Is the power supply and main tuner all one board? Is the tv chirping? From my past experience it'll do a long squeel then chirp chirp chirp. This has been posted a few times but not on your model, atleast i don't think but it always turns out to be a bad zener diode. So that would be a good place to start.

Yep, Power and Tuner are on the same board. I looked up the part number for the board but didn't find any good sources and heck, I would rather fix this one up than buy a new (or new, 'used' board) anyway. This way I know that the caps will be good caps (decent brand anyway) and that it won't be damaged in transit.

I'll post pictures tomorrow. Apparently the camera on my phone is broken (plastic lens cover/protector) is broken so there are blurry spots on the pictures. You all would probably prefer some detail in the pictures and the ones I took just don't provide such! Thanks for the prompt response though @Mr Bill! Wish I could return the request sooner.

[puttsy]

Re: Philips flat-panel dead. Replaced PSU caps and still squealing

Full board:


PSU area 1:


PSU area 2:



None of the zener dioades appear to be shorted out so it may be bad(?). Would it be easiest to replace all of them or, is there s specific one that is usually the culprit? I didn't see a D668 diode, there are several other diodes (D607, D608, D605, D606, D610) in the vascinity of the PSU. Now, would it likely be centerilized around that PSU section or, should I be looking all over the whole board for the D668 diode, if that's the common culprit?

Again, thanks for the help guys! Quite interesting.

[RON_CET]

Re: Philips flat-panel dead. Replaced PSU caps and still squealing

here's partial schematic of where D668 is located at hope this helps

[selldoor]

Re: Philips flat-panel dead. Replaced PSU caps and still squealing

As a long time lurker you should be aware that some members including myself do not like pictures posted in line, and will not even look at a thread
which has them. I suggest you edit and remove then upload using manage attachments.

[shovenose]

Re: Philips flat-panel dead. Replaced PSU caps and still squealing

As a long time lurker you should be aware that some members including myself do not like pictures posted in line, and will not even look at a thread
which has them. I suggest you edit and remove then upload using manage attachments.

@.@ they're small enough not to break the formatting of the formatting and they load instantly so seriously why does it matter?

[tom66]

Re: Philips flat-panel dead. Replaced PSU caps and still squealing

It's not a big deal. It improves the readability.

[puttsy]

Re: Philips flat-panel dead. Replaced PSU caps and still squealing

here's partial schematic of where D668 is located at hope this helps

Great! Thanks, found it. However, there is an interesting mark on the board in the vicinity of D668. Almost looks like D631 shorted out but nothing aside from the dark brown marks (almost burned or singed, but not DEEP brown/black) in it's vicinity indicates a problem. Obviously that )D668) still could be the issue but, I want your guys' opinion before I up and buy new parts that may be totally unrelated to the problem.

As for the inline pics. I know some guys hate them, others don't have a problem. I usually make sure they are within the size restrictions prior to posting but, from here-on-out, I can just attach them to help keep the crew content. Thanks!

[selldoor]

Re: Philips flat-panel dead. Replaced PSU caps and still squealing

Have you tried pinning the sound down by using a rolled up paper or thin card tube. Please can you insulate the bare mains feed - its making me queasy.

[tom66]

Re: Philips flat-panel dead. Replaced PSU caps and still squealing

Looks like this Philips uses a self-resonant two-transistor SMPS, which is a bad idea in my opinion for anything more than a couple of watts.. The squealing could be caused by one of the small poly caps on the primary side going leaky. Or it could be a shorted diode.

Is that mains lead factory issue? Looks dangerous!

[puttsy]

Re: Philips flat-panel dead. Replaced PSU caps and still squealing

Have you tried pinning the sound down by using a rolled up paper or thin card tube. Please can you insulate the bare mains feed - its making me queasy.

Looks like this Philips uses a self-resonant two-transistor SMPS, which is a bad idea in my opinion for anything more than a couple of watts.. The squealing could be caused by one of the small poly caps on the primary side going leaky. Or it could be a shorted diode.

Is that mains lead factory issue? Looks dangerous!

Absolutely NOT factory. For quick testing I tapped it onto the board. Now that more than one person has mentioned it I suppose I'll take care of it. I was actually planning on putting a jack on the case and a removable power cable but couldn't find any small figure-8 jacks lying around and didn't want the bulk of a 3-pin IEC connector on there. It's only an issue if you were to move it around but, I knew it wasn't *good* at the time, just wanted to get it tested. I nicely soldered the original cable on there after replacing the couple of caps but, after that failed, I once again took it off and just stuck that one on and off because it's a quick tap it on, tap it off to test with.

Just cut it off though, just for you guys. Now,

Looks like this Philips uses a self-resonant two-transistor SMPS, which is a bad idea in my opinion for anything more than a couple of watts.. The squealing could be caused by one of the small poly caps on the primary side going leaky. Or it could be a shorted diode.

Is that mains lead factory issue? Looks dangerous!

Any easy way to fix that or, should I *sigh* call this TV a loss and move on? I really hate to pitch it. The panel is still good on it but, I can't find a replacement board that matches the model. Any ideas on how to use the panel for anything else?